[Vwdiesel] mileage woes

[Val Christian]

On the alignment.  Anyone can align a VW front end.  A concrete floor,
a torpedo level, string (or chain), shims, a hand calculator (and a 
refresher in trig for some), shims (beer cans for Hagar), and a 
smooth road on a windless day.  Set the camber first, with the 
eccentric bolts on the struts.  (Some cars didn't come with eccentrics,
and the best thing is to upgrade.  I keep eccentrics off scrapped cars,
and you can probably buy them new.)  After you get the camber at 0
or just slightly negative (0.35 deg), and roll the car a little 
bit to verify that it is really there, then you set the toe-in.
I use a "Track Guage" which is a spring loaded rod, and chains (to 
evenly space the rod off the floor).  However, after an accident with
a sheet of plywood, when I was 16, on a family vacation, I managed to
align the 1967 Rambler American with surveyor's string.  It worked 
well enough to get the car to the Cape.  (Dad had to offload one kid
into the car, and he took the rest, and gave me $50, and the tool
box.  My 10 yo brother accompanied me.)  Oh, the plywood...it left 
a dump truck, on a bridge that we were on, and when it hit the car 
on the right front side, it lifted the car about a foot or so, and 
drove "up" the plywood.  Dad found us at the side of the road, with 
my three of my brothers and sisters white as a ghost.  The dump truck
beat it out of there.  (Boy did I digress!)

Regarding the aerodynamics...figure V**2 being the dominant factor.
Somewhere I have emphircal figures for a 1978 Diesel Rabbit I owned. 
The windows open substantially increase the drag.  The most economical
figure to operate the car at is between 40 and 45 mph.  With no wind,
40 works best.  At 40mph, in 1979, with about 60K miles on the car,
I could exceed 62 statute miles / USgal, with an outside airtemp of
50F.  (These numbers are off the top of my head, but substantially
accurate.)

Front end alignment can hurt mileage by over 10%.  On Rabbits, I tend
to find 0 camber works best for drag, and doesn't adversely impact 
handling for the driving I do.  Ditto on the rear. although it doesn't
often need alignment.  On that Rabbit, you had to drop the rear axle
to get the muffler off (one piece), so one had to realign the undercoating
marks. 

In theory the mileage would be higher at a lower speed than 40, but 
it would compromise your ability of using high gear.  On the early 
(pre 1980) Rabbits, the high gear ratio was the same for 4 speed and 
5 speed transmissions.  Things may have changed in subsequent years.

Oh, if you want to do drag calculations, a smooth road with a gradual
slope works best.  Do your testing early in the morning, before the 
wind picks up.  A topic for a different day...

Val





> 
> So now I'm looking at a total trip of between 320 and 350
> miles, using about 10 gallons. 32-35 mpg?!?! Man, was I bummed at that.
> But then I got to thinking, I was driving pretty fast there and back,
> averaging probably 70-80mph. Of course, no speedometer, so I really
> can't be sure. But I was passing a lot of people. Now I'm wondering,
> could my fast driving really have affected the mileage that much? I'm
> really hoping so!
> 
>   As Jake put it, " A Rabbit has all the aerodynamics of a flying brick"
> Kinda sums it up.  The faster you go, the more mileage it eats.  A 
> 5 speed would help.  I usually got 40mpg highway and 45 doodling 
> around semi highway and town.  It's also winter:  snow tires, denser 
> air, longer warm-up times, more idling, drag from snow, rain, slush and 
> so on.  Even more drag on the alt from heater fan, rear def. and headlights.
> 
> > 
> > Also, about what speed does the rabbit start shaking? At times, the car
> > would start vibrating, but only when I was going really fast, and the
> > engine sounded like it was about ready to rip itself to pieces (4spd
> > manual). It's got almost new tires, that were just mounted/balanced, and
> > a front end alignment just last week.
> 
>   Depends, when does the spin cycle start on yours?  ;-)  If it's shaking, 
> it's not a "normal" thing.  Figure out what tire's shaking it.  Could be a 
> bad tie rod end, lower control arm bushing, bad strut or shock, still out 
> of balance tire, out of balance drum, bad CV joint, bent axle and so on.
> Just stat eliminating things until you find a bad one, see if it fixes it 
> and keep looking if necessary.
>   A friend of mine commented that at 60mph (with a diesel and 4 speed) 
> it sounds just about ready for take-off!  It's gotta really be buzzing at 
> 80!!
> 
> > 
> > Which brings me to yet another quick question, my brother mentioned that
> > it looked like my car was driving sideways, or at least angled, when he
> > was following me. Can the rear end be out of a alignment? Can it be
> > fixed?
> > 
> 
>   Since a Rabbit kind of tapers at the rear they can look like they're 
> "crabbing" down the road when they aren't. Not to say yours isn't.  
> I've seen bent rear axles and rear wheels can be out of alignment.  
> My Jetta is currently over 2 degrees of negative camber, a bit much.
> Toe is also off.  He's ordered the shims for it, I just haven't had a chance 
> to get it back in yet.  My Rabbit was also way off on one rear.  It quit 
> "plowing" on corners after he fixed it.  Just takes shims and someone 
> that knows what they're doing with a 4 wheel alignment.
>      Loren
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